So it may seem scary that the California Department of Public Health has issued guidelines to help people "decrease their exposure to the radio frequency energy emitted from cell phones."

The department said the information was intended to help people who are concerned about health risks including brain tumours, lowered sperm counts, and effects on learning, memory, and sleep.

But California's new guidelines – and some of the news coverage they have inspired – can make it seem like using a cell phone carries far more risk than scientific evidence suggests.

Although some researchers are worried about the long-term effects of cell-phone use, so far there's not actually any evidence that the radiation emitted by smartphones causes harm.

The CDC's position is that there are no scientific findings that provide a definitive answer to the question of whether cell phone radiation causes cancer.

Most large studies documenting cancer rates haven't found significant evidence that cell phone use raises cancer rates or causes other negative health effects.

There are some good reasons to limit cell phone use, however.

What science says about cell phone radiation and health

California's department of public health suggested that people who want to reduce their risk of radiation exposure could take the following steps:

Keep the phone away from the body

Reduce cell phone use when the signal is weak (since searching for a signal could use more energy)

Reduce the use of cell phones to stream audio or video, or to download or upload large files

Keep the phone away from the bed at night

Remove headsets when not on a call

Avoiding products that claim to block radio frequency energy, since such items may actually increase your exposure

The main concern people have about cell phones is that they emit radio-frequency (RF) energy, a type of radiation.

Researchers have long wondered whether that could pose a threat to human health. But RF energy doesn't cause the DNA damage that radiation from the sun or from X-rays does, according to the National Cancer Institute. (DNA damage is the thing that leads to cancer.)

The International Agency for Research on Cancer (IARC) classifies RF energy as "possibly carcinogenic," but almost everything is "possibly carcinogenic," including coffee and pickled vegetables.

It's hard to definitively say that any substance doesn't cause cancer, even when we have evidence that substances like coffee are linked with lower cancer rates.

Researchers blasted rats with full-body doses of RF radiation (mostly at higher levels than those associated with cell phones) from the time they were born until they were two years old for nine hours a day.

They found that some male rats had higher tumour rates. But none of the control rats developed brain tumours as would have been expected, and the male rats exposed to radiation actually outlived their non-exposed counterparts.

"I'm not going to stop using my mobile phone in the light of this," Kevin McConway, emeritus professor of applied statistics at The Open University, said in a statement about that study.

However, heavy phone users who want to reduce their exposure to RF radiation in case future research reveals new risks can consider using a headset.

No reason to panic

The California guidelines describe the science as "evolving," which is accurate. It's always possible that there's some small increased risk scientists haven't identified yet.

Plus, some of the recommendations could be good ideas no matter what.

Research shows that people (especially children) don't sleep as well when they have immediate access to their phones, even if they don't use them. So keeping your phone away from the bed could help you sleep better.

Other research has shown that interruptions from phone notifications impair productivity and make people more prone to making mistakes. That means there could be other benefits to storing your cell phone in a backpack or desk instead of keeping it next to your body.